1. Field of the Invention
This invention relates to a non-contact tonometer which blows compressed fluid to an eye onto be examined to thereby deform the cornea of the eye and detects a predetermined deformed state thereof and measures the intraocular pressure of the eye to be examined.
2. Related Background Art
Heretofore, in a non-contact tonometer of this kind, compressed air has generally been used as compressed fluid. For example, as disclosed in U.S. Pat. No. 3,585,849 and European Patent No. 164,730, the air in a compression chamber is gradually compressed by a piston driven by a solenoid, and the compressed air is projected to the cornea of an eye to be examined through a nozzle and the time until the cornea becomes applanate or the internal pressure of the compression chamber when the cornea has become applanate is measured, whereafter the supply of electrical power to the nozzle is cut off. Also, in the non-contact tonometer of this kind, the measurement range is set to the order of 100 mmHg at the greatest so that even high intraocular pressure of great strength can be measured.
However, in most of ordinary eyes to be examined, the intraocular pressure is of the order of 30 mmHg at the highest and therefore, an apparatus which projects compressed fluid under more than the necessary pressure to the cornea and thereby avoids imparting excessive discomfort to the examinee has also been proposed in Japanese Laid-Open Patent Application No. 63-300740.
However, in the above-described example of the prior art, for a certain eye to be examined, change-over is effected to the measurement range for high intraocular pressure and measurement is effected. Thereafter, even if another eye is to be examined, the measurement range for low intraocular pressure is not restored as long as a particular range change-over switch is not depressed. Thus, measurement is effected in the measurement range for high intraocular pressure and if the next eye to be examined is of intraocular pressure in a range measurable in the measurement range for low intraocular pressure, excess air will be supplied to the eye to be examined to thereby impart discomfort to the examinee.
Also, in the above-described example of the prior art, in the case of an eye to be examined having high intraocular pressure exceeding this range, predetermined deformation of the cornea is not obtained as a matter of course when such eye is measured in a low measurement range and thus, measurement becomes impossible.
At this time, it is very difficult to distinguish whether the cause of the impossibility of measurement is due to an improper range of the compression pressure or unsatisfactory alignment caused by movement or blinking of the eye to be examined during measurement.